1. Field of the Invention
The present invention relates to semiconductor fabrication equipment, and more particularly, the present invention relates to an improved mechanism for de-chucking and lifting a semiconductor wafer from a chuck that resides inside a semiconductor processing chamber.
2. Description of the Related Art
In semiconductor fabrication, integrated circuit devices are fabricated from semiconductor wafers that are placed through numerous processing operations. Many of the numerous processing operations are commonly carried out in processing chambers in which layers, such as, dielectric and metallization materials are successively applied and patterned to form multi-layered structures. For example, some of these layers (e.g., SiO2) are commonly deposited in chemical vapor deposition (CVD) chambers, and then photoresist materials are spin-coated and placed through photolithography patterning. When a photoresist mask is defined over a particular surface, the semiconductor wafer is placed into a plasma etching chamber in order to remove (i.e., etch) portions of the underlying materials that are not covered by the photoresist mask.
FIG. 1A shows a semiconductor processing system 100 including a chamber 102 that is used for processing semiconductor wafers through etching operations. In this example, the chamber 102 includes a chuck 104 which is configured to support a semiconductor wafer 106. The chamber 102 is also configured to have a top electrode 114. The top electrode 114 is configured to receive processing gases which are distributed into the plasma region 112 during processing. The plasma region 112 is defined between the surface of the top electrode 114 and the surface of the wafer 106.
The top electrode 114 is also shown coupled to a match box 116a and an RF power source 118a. The chuck 104 is also coupled to a match box 116b and an RF power source 118b. The chamber 102 is provided with outlets 120 which are configured to pump out excess gases from within the chamber 102 during processing. In operation, the RF power supply 118a is configured to bias the top electrode 114 and operate at frequencies of about 27 MHz. The RF power source 118a is primarily responsible for generating most of the plasma density within the plasma region 112, while the RF power source 118b is primarily responsible for generating a bias voltage within the plasma region 112. The RF power source 118b generally operates at lower frequencies in the range of about 2 MHz.
FIGS. 1B and 1C provide a more detailed view of the chuck 104 of the semiconductor processing system 100. The chuck 104 shown in FIG. 1B is of the monopolar type in which only one positive electrode 122 is formed in dielectric material 124 and the plasma 112 potential has a negative polarity. The chuck 104 shown in FIG. 1C is of the bipolar type in which two electrodes, namely, positive electrode 130 and negative electrode 132, are formed in dielectric material 124.
As shown in FIGS. 1B and 1C, the chuck 104 contains a number of penetrations 126 through which lifting pins 128 are pneumatically actuated to lift the semiconductor wafer 106 from the chuck 104 upon completion of the processing operation. The process of removing the wafer 106 from the chuck 104 at the completion of processing is commonly referred to as a xe2x80x9cde-chuckingxe2x80x9d process. Under optimal de-chucking processes, the wafer is simply lifted off of the chuck 104 using the pneumatic controls, and can then be removed from the processing chamber 100.
FIG. 1D presents a flowchart diagram describing a conventional de-chucking operation. FIG. 1D beings at the completion of semiconductor wafer processing 140. The wafer 106 must then be allowed to fully discharge 142 before attempting to lift it from the chuck 104. For monopolar chucks as shown in FIG. 1B, wafer discharge occurs through the plasma region, and in most systems requires approximately 120 seconds to complete with minimal residual charge on the wafer 106. For bipolar chucks 104 as shown in FIG. 1C, normal wafer discharge through the plasma 112 is supplemented by discharge through the chuck 104 which is facilitated with the bipolar electrodes. Wafer 106 discharge through the bipolar chuck typically requires approximately 10 to 180 seconds. The bipolar chuck assembly is advantageous as it minimizes the time required for wafer discharge and directly improves processing cycles and throughput. However, the discharge process commonly results in residual charges that are non-uniformly distributed throughout the wafer. As will be discussed below, the presence of residual charge whether uniform or un-uniform can lead to wafer damaging repercussions.
Upon completion of wafer discharge, FIG. 1D continues with actuation 144 of the lifting pins 128 to clear the wafer 106 from the chuck 104 and allow removal of the wafer 106 from the system. Actuation of the lifting pins (typically 3 or 4) is usually achieved through use of pneumatic force. The lifting pins 128 travel upward to contact the bottom wafer surface and lift the wafer 106 to a preset transfer height. Once at transfer height, the wafer 106 is removed 146 from the system. If another wafer 106 is to be processed, the next wafer 106 is placed 148 on the lifting pins 128, lowered 150 to the chuck 104, and the process in FIG. 1D is repeated.
Lifting of the wafer 106 from the chuck 104 occasionally results in irreparable damage to the wafer 106. This damage is usually caused through contact between the lifting pins 128 and the wafer 106. If the wafer 106 contains sufficient residual charge, which is commonly non-uniform, the wafer 106 will remain electrostatically attached to the chuck 104 when the lifting pins 128 are actuated. For pneumatically actuated lifting pins 128, the lifting pins 128 are moved with a constant non-adjustable force and velocity. Thus, when impacting an immovable wafer (e.g., attached), the lifting pins will do damage to the wafer 106. If the wafer 106 is lifted only on one side (as is know to occur), the wafer 106 will slide off of the chuck 104 and become damaged. In some cases, the wafer will actually break or will cause irreversible damage to fabricated circuitry. Also, if the pin lifting force is initially resisted by the wafer 106 through residual electrostatic attraction with the chuck 104, the wafer 106 may suddenly be released from the chuck 104 as the wafer discharge process continues while the pin lifting force is applied. This sudden release from the chuck 104 may result in projectile motion of the wafer 106 and associated damage. In other cases, if the wafer 106 contains sufficient residual charge and the lifting pins 128 are applied with sufficient force, the lifting pins may actually break through the wafer.
In view of the foregoing, what is needed is a pin lifting apparatus, and method for making and implementing the apparatus which will assist in efficiently lifting the semiconductor wafer from the chuck through the application of monitored and controlled lifting force to the backside of a wafer and provide techniques for rapid removal of resistant residual charges between the wafer and chuck.
Broadly speaking, the present invention fills these needs by providing an apparatus and method for controllably lifting a wafer off of an electrostatic chuck after a processing operation. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, in a wafer processing chamber, a wafer lifting mechanism for controlling the lifting of the wafer off of an electrostatic chuck at a completion of processing is disclosed. The wafer lifting mechanism includes a pin lifter yoke that is oriented below an electrostatic chuck. The pin lifter yoke has a set of pins connected thereto, and the set of pins are configured to traverse through the electrostatic chuck and contact a bottom surface of the wafer. A link is also provided and connected to the pin lifter yoke. The link is moveable so as to cause the pin lifter yoke and the set of pins to move within the electrostatic chuck and contact the bottom surface of the wafer, and once in contact with the bottom surface of the wafer, the set of pins are capable of lifting the wafer off of the electrostatic chuck. Further included is a motor for moving the link and a force feedback system for limiting an application of force by the set of pins to the bottom surface of the wafer during the lifting.
In another embodiment, a substrate lifting mechanism for controlling the lifting of the substrate off of an electrostatic chuck at a completion of processing is disclosed. The substrate lifting mechanism includes a pin lifter yoke having a set of pins connected thereto, and the set of pins are configured to contact a bottom surface of the substrate. A lead screw is connected to the pin lifter yoke, and a motor for moving the lead screw is provided. A force feedback system is further included. The force feedback system includes a strain gauge for determining a resistive force against the set of pins, a digital signal processor for receiving data regarding the resistive force, a motor controller for controlling the motor, and an encoder. The encoder is configured to communicate lead screw position data to the motor controller and digital signal processor.
In still another embodiment, a method for lifting a wafer off of an electrostatic chuck after the completion of a processing operation is disclosed. The method includes raising a set of pins through the electrostatic chuck toward an underside of the wafer. Contact is then achieved between the set of pins and the underside of the wafer. The method then includes applying a lifting force to the underside of the wafer and monitoring the lifting force. The lifting force is then discontinued when the monitoring indicates that a threshold level has been reached.
The advantages of the present invention are many and substantial. Most notably, by monitoring the strain on the lift pins that are in contact with the wafer during lifting, it is possible to determine when the lift pins should no longer be raised so as to prevent damage to the wafer. Once the wafer has been adequately discharged and can easily be removed from the electrostatic chuck, the lifting can then resume until the wafer has been placed to its proper up position and can then be accessed by a robot""s end effector. Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.